Georgina Cano

Dynorphin A increases substance P release from trigeminal primary afferent C-fibers

Dynorphin A-(1-17) has been found to produce spinal antianalgesia and allodynia. Thus, we studied whether dynorphin A-(1-17) modulates substance P release evoked by the C-fiber-selective stimulant capsaicin (1 microM) from trigeminal nucleus caudalis slices. Very low concentrations of dynorphin A-(1-17) (0.01-0.1 nM) strongly facilitated capsaicin-evoked substance P release. This dynorphin A-(1-17) effect was not blocked by the opioid receptor antagonists naloxone (100 nM), beta-funaltrexamine (20 nM), naloxonazine (1 nM), nor-binaltorphimine (3 nM) and ICI 174,864 (N,N-dialyl-Tyr-Aib-Phe-Leu; 0.3 microM). Yet, the effect of dynorphin A-(1-17) was blocked by the NMDA receptor antagonist MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5-10-imine maleate; 0.3 microM). Neonatal treatment with capsaicin (50 mg/kg s.c.), which destroys substance P-containing primary afferents, abolished the excitatory effect of dynorphin A-(1-17) on K+-evoked substance P release. In conclusion, dynorphin A-(1-17) increases substance P release from C-fibers by the activation of NMDA receptors which supports the involvement of presynaptic mechanisms in dynorphin-induced antianalgesia and allodynia.

Opposite modulation of capsaicin-evoked substance P release by glutamate receptors

Substance P and glutamate are present in primary afferent C-fibers and play important roles in persistent inflammatory and neuropathic pain. In the present study, we have examined whether activation of different glutamate receptor subtypes modulates the release of substance P evoked by the C-fiber selective stimulant capsaicin (1 microM) from rat trigeminal nucleus slices. The selective NMDA glutamate receptor agonist L-CCG-IV (1-10 microM) enhanced capsaicin-evoked substance P release about 100%. This facilitatory effect was blocked by 0.3 microM MK-801, a selective NMDA receptor antagonist. The metabotropic glutamate receptor agonists L-AP4 (group III) and DHPG (group I) (30-100 microM) inhibited capsaicin-evoked substance P release by approximately 60%. These inhibitory effects were blocked by the selective metabotropic glutamate receptor antagonist (+/-)-MCPG (5 microM). On the other hand, AMPA and kainate (0.1-10 microM), did not significantly affect capsaicin-evoked substance P release. Thus, substance P release from non-myelinated primary afferents, and possibly nociception, may be under the functional antagonistic control of some metabotropic and ionotropic glutamate receptor subtypes.

ALTERATIONS OF EXCITATORY AMINO ACID RECEPTORS IN THE BRAIN OF MANGANESE-TREATED MICE

An excessive activation of excitatory amino acid (EAA) receptors has been associated with oxidative stress, which is considered the primary cause of manganese (Mn) poisoning neurotoxicity. Therefore, the EAA receptor distribution was analyzed by autoradiographic methods in several brain regions during Mn intoxication. We found that chronic treatment of mice with MnCl2 during 8 wk significantly alters the L-[3H]glutamate (L-[3H]Glu) binding to total glutamate (Glu) receptors, as well as to N-methyl-D-aspartate (NMDA) and quisqualate (QA) receptor subtypes. A generalized decrease of 16-24% of the L-[3H]Glu binding to total Glu receptors was found in all cortex, hippocampus, basal ganglia (except globus pallidus), and cerebellum. Saturation studies showed a significant reduction of the maximal number of receptors (Bmax) in Mn-treated mice, whereas the affinity (Kd) was not altered. L-[3H]Glu binding to NMDA sites was mainly decreased (10-21%) in a few cortical regions, basal ganglia (except globus pallidus), and hippocampus, whereas binding to QA receptor subtype was diminished (16-30%) in cortex, hippocampus, and cerebellum. The decrease of Glu receptor binding sites during Mn poisoning could reflect a receptor downregulation more than neuronal loss, since these reductions are moderate and diffuse. Thus, this down-regulation might mean a protection mechanism against an excitotoxic process associated with Mn toxicity.

Motor activity and quantitative autoradiographic analysis of muscarinic receptors in the brain of rats subjected to the forced swimming test

A cholinergic dysfunction has been involved in the neurobiological mechanisms of stress and depression. In the present study, we determined the autoradiographic distribution of muscarinic cholinergic receptors in the brain of rats subjected to the forced swimming test for 15 days. Motor activity was automatically analyzed daily before swimming. In the forced swimming test group, both total horizontal activity and ambulatory movements exhibited a significant decrease, when the data from 1st and 15th day were compared. Neither the affinity of [3H]-quinuclidinyl benzilate nor the maximal number of receptors were affected by the forced swimming test in the caudate-putamen, cortex, and hippocampus. The distribution of [3H]-quinuclidinyl benzilate binding sites did not show significant differences in the 30 analyzed areas. Further analysis of muscarinic receptor subtypes after forced swimming test would be necessary to discard any cholinergic involvement.

Multiphasic Morphine Modulation of Substance P Release from Capsaicin-Sensitive Primary Afferent Fibers

Morphine produces a multiphasic modulation of K+-evoked substance P release from trigeminal slices and dorsal root ganglion neurons in culture. We now found that the C-fiber stimulant, capsaicin (1 μM), evoked release of substance P that was inhibited, enhanced and inhibited by 0.1 nM, 1 μM, and 10 μM morphine, respectively. This morphines multiphasic effect was blocked by naloxone (100 nM). Neonatal treatment with capsaicin produced thermal hypoalgesia and abolished the multiphasic effect of morphine on substance P release evoked by 50 mM K+. These findings suggest that the multiphasic modulation of substance P release by morphine is dependent on C-type afferents and may be of relevance to nociception.

Cryptosporidiosis among patients with the acquired immunodeficiency syndrome in Maracaibo, Venezuela

Cryptosporidium is a coccidian parasite found in the intestinal and respiratory epithelia of a wide variety of vertebrate hosts. First reported in 1976 cryptosporidiosis among humans has increased dramatically since 1982. Cryptosporidium has now become one of the most common intestinal protozoa and one of the most frequent opportunistic infections in AIDS patients. Infection causes only self-limited diarrheal illness in immunocompetent persons but severe sometimes life-threatening and protracted diarrhea in immunosuppressed persons. Large-scale surveys of selected populations have found infection prevalence rates of 0.6-20% in developed countries and 4-20% in developing countries. There is however little information about cryptosporidiosis in Venezuela. The authors report findings from a preliminary study designed to evaluate the prevalence and clinical significance of Cryptosporidium in patients with AIDS in Maracaibo. Three stool specimens were collected from each of seven male and three female symptomatic patients. All were residents of Maracaibo aged 7-35 years. All had mild or severe diarrhea and some had one or more of the following manifestations: abdominal pain malaise weight loss cough with expectoration lymphadenopathy candidiasis and herpes. Four patients had Cryptosporidium oocysts associated with Trichuris trichiura and Blastocystis hominis in one case while two had only Giardia lamblia trophozoites. All cases infected with Cryptosporidium presented an inflammatory exudate replete with leukocytes plasma cells and macrophages; two cases had Charcot-Leyden crystals. This frequency of infection with Cryptosporidium is higher than that observed in the US and Brazil and similar to the frequencies reported from Africa and Haiti. The authors note that the main symptom of cryptosporidiosis is a non-inflammatory diarrhea with leukocytes rarely seen. The inflammatory exudate with abundant leukocytes observed in all of these infected patients however suggests the involvement of other associated enteropathogens and warrants further investigation.